High strength aluminum casting alloy

ABSTRACT

AN ALUMINUM CASTING ALLOY HAVING GOOD MECHANICAL PROPERTIES IS PREPARED BY ADDING, TO ALUMINUM, COPPER, MAGNESIUM, AND CADMIUM AND, ADDITIONALLY, IF DESIRED, TITANIUM AND BORON, AND, ADDITIONALLY. IF DESIRED, MANGANESE AND SILVER, SOLUTION-HEAT-TREATING THEREOF AT A TEMPERATURE HIGHER THAN 500*C., AND THEN AGEING THE SOLUTION-HEAT-TREATED ALLOY AT A TEMPERATURE BETWEEN 160*C. AND 190*C. FOR 4 TO 48 HOURS. THE ALLOY IS USEFUL IN VARIOUS TYPES OF MACHINE MEMBERS, AIRCRAFT, ROLLING-STOCK MEMBERS, ARCHITECTURAL MEMBERS, AND OTHER STRUCTURAL APPLIANCES.

United States Patent US. Cl. 148-159 4 Claims ABSTRACT OF THE DISCLOSURE An aluminum casting alloy having good mechanical properties is prepared by adding, to aluminum, copper, magnesium, and cadmium and, additionally, if desired, titanium and boron, and, additionally, if desired, manganese and silver, solution-heat-treating thereof at a tem perature higher than 500 (3., and then ageing the solution-heat-treated alloy at a temperature between 160 C. and 190 C. for 4 to 48 hours. The alloy is useful in various types of machine members, aircraft, rolling-stock members, architectural members, and other structural appliances.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a high strength aluminum alloy, and more particularly to aluminum alloys having a high tensile strength, a high yield strength and excellent toughness and also to methods for producing them.

Description of the prior art Recently, aluminum alloys having excellent mechanical properties have been needed by the various industrial fields, such as the automobile, aircraft and building industries.

Relatively high strength can be obtained by wrought aluminum alloys, but'satisfactory strength can hardly be obtained by casting aluminum alloys.

A few aluminum casting alloys have a tensile strength of about 40 kg./mm. have already been well known, but alloys having a tensile strength of 45 kg./Inm. or more are only the aluminum-zinc-magnesium system alloy.

Alloys containing a relatively high amount of zinc are very susceptible to stress corrosion cracking. An aluminum-copper-magnesium-silver casting alloy disclosed in British Pat. No. 1,090,960 has a high tensile strength of 45 kg/mm. or more, but this alloy is very expensive due to its containing silver. Therefore, the development of inexpensive aluminum casting alloys having a high tensile strength of 45 kg./mm. or more, and favorable other mechanical properties, have long been desired.

As the result of extensive studies on aluminum casting alloys having high tensile strengths, high yield strengths and toughness, and desirable resistance to hot tearing and stress corrosion cracking, it was found that aluminumcopper-magnesium-cadmium casting alloys had the aforesaid requirements.

SUMMARY OF THE INVENTION It has been known that conventional aluminum-copperrespectively. These mechanical properties are comparable 3,759,758 Patented Sept. 18, 1973 with those of the expensive aluminum-copper-magnesiumsilver alloys.

The age hardenable alloy of the present invention comprises 4.0 to 6.2% copper, 0.2 to 0.5% magnesium, 0.05 to 0.8% cadmium, 0.01 to 0.5% titanium and 0.001 to 0.01% boron, the remainder being aluminum.

The aluminum alloy of the present invention is solution-heat-treated at a temperature greater than 500 C. and aged at a temperature of from to C. for from 4 to 48 hours.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The amount of the alloying elements added to the aluminum casting alloy is within the aforesaid ranges for the following reasons.

Copper addition is essential in order to increase the strength of the alloy. Copper in an amount of from 4.0 to 6.2% is required for this purpose. The addition of copper in an amount of more than 6.2% increases the phase which is insoluble in the matrix even by the solution heat treatment, and therefore is unfavorable in order to keep the good mechanical properties and to decrease the tendency of the alloy to undergo hot tearing. For optimum results, the copper is present in an amount of from 4.7 to 5.5%.

The addition of magnesium increases the strength and the ageing property of the alloy. Magnesium in an amount of from 0.2 to 0.5% is required for this purpose. The addition of magnesium in an amount of more than 0.5 increases the tendency of the alloy to undergo hot tearing and often causes burning and quench cracking if the solution heat treatment temperature is higher, while the strength decreases if the lower solution heat treatment temperature is utilized to prevent the occurrence of hot tearing. For optimum results, the magnesium is present in an amount of from 0.2 to 0.4%

The addition of a small amount of cadmium in the aluminum-copper-magnesium alloy remarkably increases the age hardening property and the mechanical properties of the alloy, and also improves the resistance of the alloy to stress corrosion cracking. Cadmium in an amount of from 0.05 to 0.8% is requried for this purpose. The addition of cadmium in an amount of more than 0.8% increases the hot tearing tendency burning during the solution heat treatment and quenching: cracking. For optimum results, the cadmium is present in an amount of from 0.1 to 0.2% It is noteworthy that cadmium is far cheaper than silver and therefore this aluminum-copper-magnesium-cadmium alloy can be produced at far lower cost than alloys containing silver.

Titanium is beneficial in assuring both fine grain structure in the alloy and good mechanical properties through successful heat solution treatment, and in order to prevent the cause of hot tearing. Titanium in an amount of 0.01 to 0.5% is required for this purpose. The addition of titanium in an amount of more than 0.5% causes the precipitation of gross compounds which reduce the mechanical properties. For optimum results, the titanium is present in an amount of from 0.1 to 0.3%.

Boron, in an amount of from 0.001 to 0.01%, added to the alloy together with the titanium through the mother alloy or the flux, is beneficial in assuring fine grain structure.

The properties of the alloy are further improved by the addition of silver and manganese to the aluminum-coppermagnesium-cadmium alloy. The addition of a small amount of silver further increases the age-hardening properties and the mechanical properties of the alloy. That is to say, an alloy having a tensile strength of 50 kg./mm. or more, a yield strength of 45 kg/mm. or more and an elongation of 4 to 15% can be obtained. The addition of silver in an amount below 2.0% improves the mechanical properties. However, the addition of silver in an amount more than 2.0% has no more effect on the improvement of the mechanical properties. Since silver is an expensive metal, it is preferable that the amount of silver in the alloy be below 2.0%. Although the cost of the alloy becomes higher by the addition of silver, a casting requiring especially high strength can overcome such a difficult requirement.

The addition of manganese improves the resistance of the alloy to stress corrosion cracking. That is to say, the addition of manganese in an amount of below 1% in- EXAMPLE 1 Aluminum of 99.9% purity was cleaned to remove the machine oil and smut, dried and was charged into a graphite crucible and melted therein. After the temperature of the melt had reached 750 C., an aluminum-5% titanium mother alloy Was added to the melt. Then, copper was added to the melt at 750 C. and the melt was stirred. After that, cadmium wrapped in aluminum foil and magnesium were added to the melt at 730 C. and

creases the resistance to stress corrosion cracking without o decreasing the mechanical properties, but an amount of 750 fespectlvelymanganese greater than 1% does not have the desired effect. For optimum results, the manganese is present A flux cnta1mng tltan1um and boron in an amount of below 0.5% (K2T1F6+KBF4+C2C16) It is desirable to use aluminum of as high a purity o as possible for the production of the aluminum-coppergi g gi s i to l g: g magnesium-cadmium alloy in order to obtain an alloy O 0 ase 6 3 u i i having high strength and toughness; the iron and silicon .3 e o i 9 E g owe i content of the alloy are desirable below 0.2%. The i 6) i PHIL; 6 me y means 0 optimum ranges of the content of the alloying elements 5 p 081) onzer to egasst eme a The resultant melt held at 750 C. for minutes was of the alloy are as follows.

Percent sub eCted to a gas generating test by pouring about 200 g. of the melt into a preheated isolite mold, solidifying the Copper 4.7 to 5.5

melt under a reduced pressure of about 5 mm. Hg, and Magnesium 0.2 to 0.4

observing the generation of gas from the solidifying melt. Cadmium 0.1 to 0.2 30 Titanium 0 1 to 0 3 After confirming the lack of gas generation by means of the test, the dross was removed from the melt surface Boron .-Below 0.01

and the melt was poured into a test permanent mold. The 'fllumlmlm Y 0f the pliesellt lnvfintlon 18 heat- The casting test pieces were solution-heat-treated at 530 treated 111 the followll'lg maflner- C. for 12 hours, quenched into cold water and aged at The solution heat treatment must be carried out at a 1 5 for 32 h temprafllfe higher thal} for a time Suificient The test pieces were subjected to a tensile test and to dissolve the deposited copper-rich compound fully h i l l i and uniformly into the matrix. The solution heat-treating Th lt were as follows; tensile strength 48.6 kg./ temperature is preferably selected as high as possible with- 40 2 yield Strength (02% ff t) 435 2; elongw out causlng Purnmg or q e crackmg- The upp limit tion 0.0%; chemical composition; Cu 5.37%, Mg 0.33%, of the solution heat-treating temperature is determined Cd 0.13%, Ti 0.16%, B 0.004%, Fe 0.07%, Si 0.05%, by the content of the alloying elements, especially d b l AL cadmium and magnesium. The aluminum alloy having EXAMPLE 2, the above preferred composition is satisfactorily solution-heat-treated at 530 C. for 12 hours. An aluminum alloy melt was produced according to the The water quenching after the solution heat treatment same melting and alloying procedures as in Example 1. Gas must be carried out as rapidly as possible. The temperawas removed from the melt by injecting a gas mixture of ture of the water after quenching must not exceed C- chlorine and nitrogen through the melt with a graphite The quenching temperature for intricate castings having 50 pipe. The test pieces cast in the mold were solution-heatparts of different thicknesses is preferably 5 to 10 C- treated at 525 C. for 6 hours, quenched into cold water lower than the ordinary solution heat-treating temperaand aged at 180 C. for 16 hours. The tensile strength, ture, thus preventing internal strain or cracking during yield strength (0.2% offset), elongation and chemical the quenchlflg OPBTaUOH composition of the resultant alloy were as follows: tensile The precipitation heat treatment of this aluminum alloy t h 47,0 k i ld trength 40 6 kg /mrr1. is carried out at a temperature of about to 190 C. e1ongation 95%; he i l composition; Cu 4.83%, Mg for4to 48 hours. 0.31%, Cd. 0.11%, Ti 0.02%, B 0.003%, Fe 0.07%, Si

Maximum strength is obtained by ageing at C. (104% d b l 1 for 20 hollrS- A high y f Strength is Obtained y ageing The titanium in the alloy was derived not from the for a longer time at a higher temperature, whereas a high 60 lu in -titaniu alloy but fr m the refining flux. elongation is obtained by ageing for a shorter time at a Table 1 shows the chemical compositions of aluminum lower temperature. alloys of this invention and those of conventional high In the case of requiring a high elongation while sacrificstrength and heat resistant aluminum casting alloys.

TABLE 1.-CHEMICAL COMPOSITION Alloy No. On Mg Cd T1 B Fe Si Ni Mn Ag Al 3 --4.99 0.30 0.17 0.10 0.003 0.07 0.04 Balance 4 0.34 0.14 0.10 0.004 0.07 0.05 Do. 5.. .40 0.28 0.10 0.002 0.03 0.04 D0. 0 4.15 0.30 0.59 0.10 0.003 0.07 0.05 Do. 7 4.05 0. 29 0.14 0.32 0.003 0. 00 0.05 Do. 8 5.11 0.30 0.10 0.21 0.004. 0.07 0.04 Do. 9.-. .34 0.10 0.17 0.003 0.07 0.04 Do. 10 .31 0. 0 0.17 0.003 0.07 0.04 Do. 11 0.17 0.20 Do. 12 0 0.00 0.04 D0. 13 0.002 0.05 0.03 Do. 14 5. .28- 0.19 0.003 0.002 0.002. 0.00 D0.

1 Conventional aluminum alloys.

Table 2 shows the heat treatment conditions and the mechanical properties at room temperature of the alloys tabulated in Table 1.

2. A method of heat-treating a high strength aluminum casting alloy, said alloy consisting of from 4.7 to 5.5% copper, from 0.2 to 0.4% magnesium, from 0.1 to 0.2%

TABLE 2.HEAT TREATMENT CONDITIONS AND MECHANICAL PROPERTIES AT ROOM TEMPERATURE Tensile Yield Elon- Solution heat Quenching strength, strength, gation,

Alloy No. treatment liquid Ageing treatment kg./mm. kg. /1mn. percent 3 530 0. X8 hoursn Cold water 165 (1X28 hours 47.6 41. 7 8.7 4. 530 C.Xl2 hours d 165 C. 32 hours.... 47. 5 42. 3 5.0 5. 520 C. 6 hours do 176 (1X20 hours 46. 0 40. 6 7. 2 6 -do 1o. 180 C. 16 hours--. 45. 1 39. 1 8. 1 7. 530 C.X12 hours.-- do 165 C. 28 hours.-. 45. 9 39. 7 10. 2 8 0 -do 165 (1X24 hours.... 51. 8 46. 9 9. 5 9 do dn 165 C.X28 hourS 46. 6 39. 7 7. 8 10 do do 165 (1X24 hours 51. 0 4G. 2 8. 6 11 515 C.X6 hours d0 170 C.X12 hours..- 40.4 33. 3 8.2 12 530 C.X4 hoursdo 175 C. 16 hours 42.1 34. 4 11.1 13 1 525 C.X12 hours... do 160 C.X hours 47. 0 41. 5 l0. 4 14 .do "do do 18.3 43.9 7.2 15 520 (LXG hours 70 O. water 170 C.Xl5 hours-- 35. 9 35. 9 0.4

1 Conventional aluminum alloys.

Table 3 shows the mechanical properties at elevated temperature of the alloys shown in Tables 1 and 2.

TABLE 3.-MECHANICAL PROPERTIES AT ELEVATED TEMPERATURE Mechanical properties Alloy No. 100 0. 200 C. 250 C. 300 C a T.S., lgg.lmm. 4s. 4 34. 6 26.6 18.2

Y.S., kg ./mm. 40. 8 34. 5 26. 5 17. E., percent 9. 8 9. 7 9. 3 9.1

18 T.S., kg./mrn. 42.0 34.4 26.9 18.4 Y.S., kg./mm. 38. 6 33. 7 26. 5 17. 8 13., percent 10.9 10. 7 10.1 10.6

15 T.S., kgJInmA.-. 32.5 31.0 25.8 16.5 Y.S., kg./mm. 32. 5 29. 8 24. 4 15. 2 E., percent 0.4 0.7 1. 3 3. 2

It is evident from Tables 2 and 3 that the aluminum alloy of the present invention has excellent mechanical properties not only at room temperature but also at elevated temperatures.

As mentioned above, the aluminum casting alloy of this invention can be produced at low cost and has excellent mechanical properties as compared with those of conventional aluminum alloys, and therefore can be applied to various types of uses; e.g., as machine members, aircraft members, rolling-stock members, architectural members and other structural appliances.

What is claimed is:

1. A high strength aluminum casting alloy consisting of from 4.7 to 5.5% copper, from 0.2 to 0.4% magnesium, from 0.1 to 0.2% cadmium, from 0.1 to 0.3% titanium and not more than 0.01% boron, not more than 0.5% manganese, not more than 0.2% iron and silicon, the balance being aluminum,

said alloy having been solution-heat treated at a temperature of at least 500 C., and for a time sufficient to dissolve the deposited copper-rich compounds into the matrix of said alloy, and subsequently aged at a temperature of from 160 C., to 190 C., for a period of time ranging from 4 to 48 hours.

cadmium, and not more than 0.1% boron, not more than 0.5 manganese, the balance being aluminum, said method comprising solution-heat treating said alloy at a temperature of at least 500 C. and for a time sufficient to dissolve the deposited copper-rich compounds into the matrix of said alloy, quenching said alloy and then ageing said alloy at a temperature of from 160 to 190 C., and for a period of time of from 4 to 48 hours.

3. A method of heat-treating a high strength aluminum casting alloy, said alloy consisting of from 4.7 to 5.5% copper, from 0.2 to 0.4% magnesium, from 0.1 to 0.2% cadmium, from 0.1 to 0.3% titanium, not more than 0.01% boron, not more than 0.5% manganese, not more than 0.2% iron and silicon, the balance being aluminum, said method comprising solution-heat-treating said alloy at a temperature of at least 500 C. and for a period of time suiiicient to dissolve the deposited copper-rich compounds into the matrix of said alloy, quenching said alloy in cold water wherein the temperature of the water after quenching does not exceed 50 C., and ageing said alloy at a temperature between 160 and 190 C. for from 4 to 48 hours.

4. The method as in claim 3, wherein the temperature of said solution-heat-treatment varies from 520 to 530 C. for a period of time of between 6 and 12 hours, and wherein said ageing varies from a temperature of 165 to 180 C. for a period of time of 16 to 32 hours.

References Cited UNITED STATES PATENTS 3,287,185 11/1966 Vachet et a1. 75-142 3,347,665 10/1967 Miller 6101 75-142 3,414,406 12/1968 Doyle et a1. 75 142 3,475,166 10/1969 Raflin 75-142 RICHARD O. DEAN, Primary Examiner US. Cl. X.R. 

